The heat battery is based on an old thermochemical principle, which is that when water is added to salt it produces heat. The reverse is also possible, whereby heat can be used to evaporate the water, thus storing the heat energy inside the salt. Storing heat within dry salt makes the battery completely loss-free, providing an incredibly efficient way to store energy for future use. This is particularly useful when energy supply is coming from renewable sources, such as wind and solar, which...